Acylated amino acid silver salts



patented May 13, 1952 ACYLATEZ-D AMINO ACID SILVER SALTS Francis M. Whitacre, Manhasset, and Dina Van Praag, New York, N. Y., assignors to Schiefielin & 00., New York, N. Y., a corporation {of New York No Drawing. Application June 14, 1948,

SerialNo. 32,993 r Claims.

This invention relates to chemotherapeutic agents or compounds active against pathogenic micro-organisms and more particularly to compounds comprising the silver salts of the acylated essential alpha-amino acids. By the expression essential alpha-amino acids" it is intended to include those grouped together as such on the rat basis, which are: lysine, tryptophane, methionine, histidine, phenylalanine, leucine, iso-leucine, threonine, valine and arginine. A preferred class of acids comprises the acylated essential sulphur-containing alpha-amino acids.

One of the advantages of the invention is that it provides efiective chemotherapeutic agents in a form which is readily assimilable by pathogenic micro-organisms and which, in addition, are essential in their metabolism. In the preparation of the agents, the amino acids described above are the starting materials, and an acyl group is introduced, in the amino group of the acids. The acyl group may be cyclic or acyclic, saturated or unsaturated, and in addition may be substituted by other groups such as the halogen, hydroxyl, keto, amino etc. groups. For example, the acyl group may be acetyl, propionyl, butyryl, benzoyl, salicylyl, etc. The acylated acid is then isolated from the reaction mixture and reacted with a suitable silver salt. The following are examples of specific silver salts of acylated essential alpha-amino acids: silver acetyl methionine, silver'propionyl methionine; silver salicylyl methionine, silver acetyl leucine, silver acetyl tryptophane, silver butyryl methionine, silver butyryl tryptophane, silver benz-oyl leucine, silver acetyl lysine, silver propionyl histidine, etc. Examples of the preparation of a few compounds are as follows:

Example 1 Ten gms. of l-leucine were dissolved in 20 cc. water and 20 cc. of 2 N caustic soda and kept in an ice bath. A mixture of 1 cc. of propionyl anhydride and cc. of 2 N caustic soda was added, with stirring, about every 5 minutes. untilten such additions had been made. The reaction mixture was left to stand at room temperature for a while, and then 40 cc. of 6 N sulfuric acid was added, whereupon a heavy white precipitate of propionyl leucine was formed. The precipitate was recovered and dissolved in water. Then a solution of sodium bicarbonate was added to a silver nitrate solution to form a precipitate of silver carbonate, which was separated. The solution of propionyl leucine was poured over the solid silver carbonate to form a clear solution of the silver salt of propionyl leucine, The salt was recovered from the solution by evaporating the latter on the steam bath under reduced pressure. It has the formula:

CHaCI-I(CH3) CH2CH(NH.COCH2CH3) COOAg.

Example 2 Ten gms. of methionine weredissolved in 2%) cc. water and 35 cc. of 2 N caustic soda and placed in an ice bath. A mixture of 2 cc. of propionyl anhydride and 20 cc. of 2 N caustic soda was added, with stirring, at intervals of about 5 minutes until eight additions were made. The resulting mixture was left to stand at room temperature fora While. Then 65 cc. of; 6 N sulfuric acid was added to the mixture. The propionyl methionine, which was formed was extracted from the solution. as follows: the sodium sulfate which was formed was salted out with 800 cc. of ethanol and. the mixture filtered. The

ethanol was distilled off, and the residue was ex-.

tracted with hot ethyl acetate. On cooling, fine white crystals of propionyl methionine were formed. The latter was then dissolved in water and poured over silver carbonate to form a solution of silver propionyl methionine. The salt was recovered from the solution by evaporation on the steam bath under reduced pressure. Its formula is:

Fifty gms. of acetylsalicylic acid, or aspirin, were placedv in a 500 cc. flask, 50 cc. of thi'onyl chloride were added and then 3 to 4 drops of pyridine, following which the mixture was placed on a steam bath until a clear, deep brown, liquid was formed. The excess of thionyl chloride was removed by distillation. The remaining material was extracted three times with 25 cc. portions of anhydrous benzene. The benzene was then distilled from the extract, leaving acetylsalicylic chloride. Four gms. of methionine were then dissolved in cc. of water and 20 cc. of 2 N caustic soda, while cooling and stirring. At 5-minute intervals, eight additions of 20 cc. of 2 N caustic soda containing 1 cc. of acetylsalicylic chloride were made to this solution. The resulting mixture was heated on a steam bath, then cooled to room temperature, and 33.5 cc. of 6 N sulfuric acid were added. An oily-solid precipitate, salicylyl methionine, was formed, which was finally crystallized from water. M. P. 117-1l8 C. Thereafter it was dissolved in 1 N caustic soda solution and a solution of silver nitrate added thereto to form the silver salt of salicylyl methionine which precipitated out from the solution. Its formula is:

cine, a clear solution of silver acetyl leucine being formed. The excess of the silver carbonate was separated by decantation, and the solution of silver acetyl leucine evaporated to dryness under reduced pressure. It has the formula:

CH3CI-I(CH3) CH2CH(NH.COCH3) COOAg Example Ten gms. of methionine were dissolved in 20 cc. of water and 20 cc. of 2 N caustic soda and then cooled in an ice bath. Ten additions of cc. of 2 N caustic soda and 1 cc. of acetic anhydride were made, each at 2-minute intervals. The solution was then left to stand at room temperature for a while and 40 cc. of 6 N sulfuric acid was added. After removal from the solution of the water and excess acetic anhydride by vacuum distillation, acetyl methionine was extracted with hot absolute ethyl acetate. The ethyl acetate was then evaporated and acetyl methionine was recrystallized from a minimum amount of ethyl acetate. M. P. ll4-l15 C. A half gram of acetyl methionine was next dissolved in water. Silver carbonate, freshly prepared by adding 1 gm. of sodium bicarbonate to 1 gm. of silver nitrate solution, was then added to the latter solution. The excess silver carbonate was separated by decantation, and the clear solution of silver acetyl methionine evaporated under reduced pressure.

Example 6 Five gms. of tryptophane, 10 cc. of water, and

cc. of 2 N caustic soda were mixed while stir-' ring and cooling to about 0. Six additions of 10 cc. of 2 N caustic soda and 1 cc. of acetic anhydride were added at intervals of about 2 minutes. Then cc. of 6 N sulfuric acid were added, and after standing for a while at room temperature, acetyl tryptophane precipitated out. M. P. 203-204 C. Silver carbonate, prepared as described in Example 5, was then added to asolution of acetyl tryptophane, and the excess of silver carbonate separated by decantation. The resulting clear solution of silver acetyl tryptophane was evaporated under reduced pressure.

The compounds of the invention have shown themselves to be active against such 1 microorganisms as Staphylococcus aureus, Eberthella typhosa, trichomonosa, vaginalis, etc. By reason of its special activity, the preferred compound is silver propionyl methionine.

While the invention has been described in connection with more or less specific embodiments, it will be appreciated that it is capable of obvious variations without departing from its scope.

In the light of the foregoing description, the following is claimed:

1. As a chemotherapeutic agent active against pathogenic micro-organisms, a silver salt of an acylated essential sulphur-containing alpha-amino monocarboxylic acid of the formula wherein R is the residue of the essential sulphurcontaining amino acid and R is an acyl group.

2. As a chemotherapeutic agent active against pathogenic micro-organisms, a silver salt of acylated methionine having the formula CHQSCH CHzOHCOOAg HNR wherein R is an acyl group. 7

3. As a chemotherapeutic agent active against pathogenic micro-organisms, the silver salt of acetyl methionine having the formula cmscmomonoooll HNCOCHa.

4. As a chemotherapeutic agent active against pathogenic micro-organisms, the silver salt of propionyl methionine having the formula CHsSCHzCHzOHCOOAg HNO 0 CHZCHS 5. As a chemotherapeutic agent active against pathogenic micro-organisms, the silver' salt of salicylyl methionine having the formula CHaSCHzCHzCHC O OAg EN 0 o 06H; OH FRANCIS M. WHITACRE. DINA VAN PRAAG;

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,161,866 Kautzsch Nov. 30, 1915 2,250,553 Ruskin July 29, 1941 FOREIGN PATENTS Number 9 Country Date Germany July 29, 1912 OTHER REFERENCES 

1. AS A CHEMOTHERAPEUTIC AGENT ACTIVE AGAINST PATHOGENIC MICRO-ORGANISMS, A SILVER SALT OF AN ACYLATED ESSENTIAL SULPHUR-CONTAINING ALPHA-AMINO MONOCARBOXYLIC ACID OF THE FORMULA 